This invention relates to transition metal complexes, and more particularly to neutral, luminescent complexes having rectangular structures.
The desirability of neutral molecular rectangles for molecular recognition and separation applications has been previously reported (Belanger et al., J. Am. Chem. Soc., 121:557-563, 1999).
Supramolecular structures containing transition metal ions with potential inclusion and host-guest applications have been extensively explored in recent years (Stang et al., J. Chem. Commun., 1453-1454, 1997; Stang et al., J. Am. Chem. Soc., 117:6273-6283, 1995; Stang et al., Organometallics, 13:3776-3777, 1994; Caulder et al., J. Chem. Soc., Dalton Trans., 1185-1200, 1999; Fujita et al., Bull. Chem. Soc. Jpn., 69:1471-1482, 1996; Fujita et al., Tetrahedron Lett., 32:5589-5592, 1991; Lehn et al., Supramolecular Chemistry: Concepts and Perspectives, VCH: Weinheim, 1995; Drain et al., J. Chem. Soc., Chem. Commun., 2313-2315, 1994). Stang and co-workers contributed to the formation of a combinatorial library of cyclic molecular polygons via the systematic combination of building blocks with predetermined angles (Olenyuk et al., J. Chem. Soc., Dalton Trans., 1707-1728, 1998).
The initial focus was directed toward molecular squares, i.e., macrocycles fabricated by cis-coordinated transition metal comers and rigid or semirigid bifunctional ligand edges (Fan et al., J. Am. Chem. Soc., 121:2741-2752, 1999; Stang et al., Angew. Chem., Int. Ed. Engl., 35:732-736, 1996; Stang et al., Acc. Chem. Res., 30:502-518, 1997; Belanger et al., supra; Slone et al., Coord. Chem. Rev., 171:221-243, 1998; Slone et al., J. Am. Chem. Soc., 117:11813-11814, 1995; Sun et al., Inorg. Chem., 38:4181-4182, 1999).
Subsequent efforts were devoted to the synthesis of molecular rectangles to improve selectivity and sensitivity in molecular recognition and separation (Benkstein et al., Inorg. Chem., 37:5404-5405, 1998; Benkstein et al., J. Am. Chem. Soc., 120:12982-12983, 1998; Slone et al., Inorg. Chem., 35:4096-4097, 1996; Woessner et al., Inorg. Chem., 37:5406-5407, 1998). Hupp et al. were the first to report the preparation of rhenium thiolate-based rectangles that exhibited interesting electrochemistry. Subsequent work by the same group led to the synthesis, characterization, and preliminary binding properties of a new class of tetracationic rectangular molecules with triflate as counterion (Benkstein et al., supra). To tune the cavity size, Sullivan et al. recently also reported the preparation of a series of molecular rectangles based on fac-Re-(CO)3 comers containing 4,4xe2x80x2-bipyridine as one side and two xcex72-alkoxy or hydroxy bridges as the other (Woessner et al., supra).
All molecular rectangles reported thus far have had a net charge, however, and thus required counterions within their channels. Past attempts to make neutral rectangles have exclusively yielded molecular squares (Benkstein et al., supra).
Accordingly, a need exists for a method of preparing neutral molecular rectangles.
The invention is based on the discovery that a new class of molecular rectangles can be prepared by using a stepwise synthesis plan under mild temperature conditions. The new rectangles are neutral and exhibit luminescence in solution at room temperature.
In general, the invention features a compound having the structure: 
where M is a transition metal; A and B, indepedently, are neutral bidentate ligands; n is 1, 2, 3, or 4;m is 0, 1, or 2; and X is chlorine (Cl), bromine (Br), or iodine (I).
M can be, for example, iron (Fe), ruthenium (Ru), or osmium (Os), in which cases, n and m can each be 2; rhenium (Re) or manganese (Mn), in which cases n can be 3, and m can be 1; or chromium (Cr), molybdenum (Mo), or tungsten (W), in which cases n can be 4, and m can be 0.
A and B can be, independently, unsubstituted or substituted 4,4xe2x80x2-polypridyl ligands, or can be selected from the group consisting of: 
and substituted derivatives thereof.
In some cases, X is Br, A is 
and B is 
In other cases, X is Br, A is 
and B is 
In still other cases, X is Br, A is 
and B is 
The invention also features a method of making a compound having the structure: 
where M is a transition metal; A and B, indepedently, are neutral bidentate ligands;
n is 1, 2, 3, or 4; m is 0, 1, or 2; and X is Cl, Br, or I. The method features the steps of: (a) reacting M(X)m(CO)n+2 with trimethylamine N-oxide in the presence of acetonitrile to form: M(X)m(CO)n+1(NCCH3); (b) reacting M(X)m(CO)n+1(NCCH3) with bidentate ligand A to form: (CO)n+1(X)mMxe2x80x94Axe2x80x94M(X)m(CO)n+1; (c) reacting (CO)n+1(X)mMxe2x80x94Axe2x80x94M(X)m(CO)n+1 with trimethylamine N-oxide in the presence of acetonitrile to form: (CH3CN)(CO)n(X)mMxe2x80x94Axe2x80x94M(X)m(CO)n(NCCH3); and (d) reacting (CH3CN)(CO)n(X)mMxe2x80x94Axe2x80x94M(X)n(CO)n(NCCH3) with bidentate ligand B to form the compound having the structure: 
The invention also features a method for forming a thin film on a substrate. The method includes the steps of: (a) preparing a solution of a molecule rectangle of claim 1; (b) dip coating or spraying the substrate with the solution; and (c) drying the substrate to form a thin film of the molecular rectangle on the surface of the substrate. The substrate can be, for example, an electrode such as a gold or glassy carbon electrode.
The invention also features a method for differentiating redox substances of different sizes. The method includes the steps of: (a) coating an electrode with a molecular rectangle of claim 1; and (b) measuring the redox potential of a solution to differentiate redox substances present in the solution.
The invention also features a method for separating metal coordination complexes. The method includes the steps of: (a) coating an electrode with a molecular rectangle of claim 1; and (b) passing a solution containing metal coordination complexes through the coated electrode while applying a potential, to separate the coordination complexes.
The invention also features a method for photodegradation of chemicals. The method includes the steps of: (a) treating the chemicals with a solution comprising vitamin B12 and a molecular rectangle of claim 1; and (b) photoactivating the molecular rectangle by UV irradiation to form an active species that reduces vitamin B12 to a species that degrades the chemicals. The chemicals can include, for example, one or more haloalkanes.
As used herein, the terms xe2x80x9crectanglexe2x80x9d and xe2x80x9cmolecular rectanglexe2x80x9d refer to transition metal complexes having four metal atoms M connected in a rectangular geometry via two pairs of bridging ligands (i.e., 2 A and 2 B). Optionally, additional ligands L can be attached to the metal atoms. Such rectangles are generally depicted by the formula: 
The invention provides several advantages. For example, the new molecular rectangles exhibit luminescence in solution at room temperature. Since the luminescence of these molecules is sensitive to the environment, the new rectangles can be used as luminescent sensors. Changes in the environment of the molecules can be detected by monitoring changes in luminescence intensity or lifetime.
Host-guest chemistry is an important area of study in the field of supramolecular chemistry. Many of the previously reported rectangles have been charged and have had small cavities. Counterions can become trapped inside the cavity of charged rectangles, and can thereby interfere with host-guest chemistry or affect molecular sensing properties. In contrast, the new molecular rectangles are neutral and have no counterions inside their channels. The new molecular rectangles also possess large cavities, making them suitable as hosts for many molecules of varying sizes, or for use in inclusion studies.
Molecular rectangles can exhibit greater selectivity with respect to molecular size than can squares, allowing them to find use in molecular sieves.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.